Bald Eagles: Productivity and Contaminants
Relations

The number of bald eagles (Haliaeetus leucocephalus) nesting
along the lower Columbia River has doubled in the
last six years, yet many of these pairs are not reproducing normally.
Productivity averages are well below statewide values for eagles
nesting in other areas of Oregon and Washington. While productivity
of these eagles is low, nesting success in other areas of the two
states is close to the goals established to delist the species
from the Federal Endangered Species list.

In 1994-95, we collected bald eagle eggs from nests along the
lower Columbia River and evaluated eggshell thickness and analyzed
egg contents for organochlorine pesticides, total polychlorinated
byphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated
dibenzofurans (PCDFs), and the dioxin-like planar PCBs. Bald eagle
productivity and egg contaminant results from 1994 to 1995 were
compared to a previous study to evaluate changes over time.

We found that recent increases in productivity averages were
due to new pairs nesting along the river, yet productivity at 23
older breeding areas remained low and was not different between
the two study periods. Eggshells averaged 11 percent thinner than
shells measured prior to the use of the pesticide DDT. DDE and
total PCB concentrations decreased in eggs from older breeding
areas between the two study periods, but concentrations were still
above values associated with poor productivity. Dioxin equivalents
(TEQs) exceeded estimated no-effect values for bald eagles during
both studies.

Although total productivity has increased due to
the success of new nesting pairs moving into the region, results
indicate that
organochlorine contaminants continue to impact the breeding success
of lower Columbia River eagles. The greatest impact appears to
occur at older breeding territories, which were located predominantly
in the lower estuary below river mile 60. Eagles nesting toward
the mouth of the river may be at greater risk of exposure to some
dioxin-like compounds, and the reproductive success of some new
pairs nesting in this area could be impacted in the future. Complete
report.